MOST CLASSES OF DORSAL-ROOT GANGLION NEURONS ARE SEVERELY DEPLETED BUT NOT ABSENT IN MICE LACKING NEUROTROPHIN-3

During development, many neurons in the dorsal root ganglia require ne urotrophin-3 for survival.(5,7,24,25) However, it is not known precise ly which subpopulations of sensory neurons, other than the propriocept ive afferents,(5,7,24) are neurotrophin-3 dependent in vivo. In this s tudy, using a battery of neurochemical markers that label different su bpopulations of dorsal root ganglion neurons, we found a widespread, a bout 60-65% loss of cells in most subpopulations in neurotrophin-3 def icient mice.(1) Intermediate losses were found in the heterozygous mut ant mice consistent with a gene dosage effect, In agreement with this, the cell size distribution between the homozygous mutant and wild typ e mice was virtually identical, The loss of small neurons containing c alcitonin gene-related peptide, substance P and thiamine monophosphata se activity suggests that many unmyelinated primary afferents are also lost in the mutant animals, The fact that many different sensory neur on subpopulations are lost to the same extent in neurotrophin-3 defici ent mice is consistent with the proposed early role of neurotrophin-3 during neurogenesis.(3,8,11,12,15,18,21,24,27) Interestingly, calretin in immunoreactive neurons, which contribute a minor subpopulation, wer e not affected suggesting that neurotrophin-3 independent regulation o f neurogenesis occurs in addition to prominent neurotrophin-3 dependen t mechanisms. Copyright (C) 1966 IBRO.